Opal Mineral Collection - Height: 4.2 cm - Width: 5.8 cm- 36 g - (1)

Opal is an amorphous colloidal mineral, composed of hydrated silica: (SiO2·nH2O), semi-amorphous or microcrystalline, i.e., lacking a lattice structure; in fact it does not appear as crystals, but in veins, nodules and crusts of various colors, often with iridescence. The color ranges from transparent to milky white, with an infinity of different intermediates (green, red, yellow, brown, black). The water content can reach up to 20%. The formation of Opal occurs through the slow geological deposition of a colloidal silica gel at low temperature. It includes many varieties, among which common opal, precious opal, black opal, water opal, fire opal, opal-xyloid, and illite. The word “Opal” has a common root in Sanskrit ùpala, in Greek ὀπάλλιος opallios, and in Latin opălus (meaning “precious stone”).